A viable process to produce titanium powder entails the following overall reaction:TiCl4+2mM=Ti+2mMCl2/m wherein,
M is a reducing agent selected from an alkali metal or alkaline earth metal, for example, Li, Na, K, Be, Mg, Ca, and the like, however, in practice M is typically selected from the group Li, Na, Mg, and Ca; and
m=1 when M is an alkaline earth metal and 2 when M is an alkali metal.
This reaction can be performed continuously in a molten salt medium that consists mainly of a halide salt of the reducing agent, typically a chloride salt, which is also a by-product of the reaction.
The titanium thus produced is in the form of powder that is suspended in the molten salt medium. This can be separated from the molten salt by a number of different known technologies such as filtration, sedimentation, leaching or evaporation or any combination of these technologies. After separation, the salt can be recovered and electrolyzed by conventional means to regenerate the reducing agent and chlorine gas, e.g.:MCl2/m=M+1/mCl2 
The reactor or reactors in which the reaction is performed is made of a suitable metal, preferably a low-alloy steel vessel.
A major problem experienced with the process is that the TiCl4 is reduced so rapidly that it forms lumps of titanium powder that blocks the line through which the TiCl4 enters the reactor vessel and it also forms lumps of fine agglomerated titanium particles that adhere to the reactor wall and reactor internals such as baffles and stirrers.
It is believed that this rapid reaction occurs via electrochemical reactions which allow the TiCl4 and subsequent titanium sub-chlorides to react with the reducing agent even if there is no physical contact between the titanium chlorides and the reducing agent. This process is sometimes referred to as long range electronically mediated reduction (LR-EMR).
The major electrochemical reactions that occur are:
Anodic Reactions:M=Mn++ne−TiCl2+Cl−=TiCl3+e−Cathodic Reactions:TiCl4+e=TiCl3+Cl−TiCl3+e=TiCl2+Cl−TiCl2+2e−=Ti+2Cl−
The electrons that are formed via any one of the anodic reactions are conducted along all or any of the metal parts of the reactor and wherever gaseous TiCl4 or any dissolved titanium chloride species are in simultaneous contact with such metal parts and the molten salt reaction medium, it is reduced with the electrons. The reducing metal cations and chloride anions that are formed as a result of these reactions neutralize each other via the salt bridge formed by the molten salt medium in the reactor.
It has been proposed to do the reduction of TiCl4 in two batchwise stages in a single alumina crucible reactor. In the first stage TiCl4 is reduced with metallic Ti to a titanium sub-chloride (TiCl3 or TiCl2, preferably TiCl2) and in the second stage, the sub-chloride is reduced with a reducing metal to metallic titanium powder. Part of the metallic titanium produced in the second step is recycled to the first step and the rest is withdrawn as product.
The two stage process was demonstrated on a laboratory scale by doing the first step, batch wise in an alumina crucible and feeding the TiCl4 into the alumina crucible via an alumina or a magnesium oxide tube and thereafter, carrying out the second step batch wise in the alumina crucible by adding magnesium to TiCl2 containing molten MgCl2.
By doing the experiments in an alumina crucible, the electrical current path was essentially broken and by doing the experiments batch-wise in two stages and at different times, the molten salt bridge between the magnesium (or reducing metal) and the TiCl4 feed line was broken.
However, when using an alumina lined reaction vessel with some of the more reactive reducing agents, alumina reacts with the reducing agent and it is virtually impossible to produce titanium meeting the industrially required oxygen specification because the alumina is too reactive. The only oxides that can be used that are sufficiently inactive to the relevant reducing agents noted are calcium, scandium and yttrium oxide. Unfortunately these oxides are too inconvenient or expensive to use as lining material. Furthermore, batch-wise production of titanium powder would be more expensive than continuous production.
Thus, having considered the above technical problems in the production of titanium powder the inventors now propose the following invention.